Justin Marshall's Chalkboard: Carter vs Nonu

Dan Carter and Ma'Nonu face off on Saturday night. Photo /Getty Images

The Blues clash with the Crusaders was already shaping as the most mouth-watering clash of the round, and that was before Dan Carter was selected to play at second five-eighth.

I believe Carter is capable of being a world-class No 12 - he has no qualms about taking the ball to the line and is a good defender.

This will be the first time in a long time Carter has played a significant stakes game of rugby in the No 12 jersey and it just so happens it is against a team who has the world No 12's best second-five: Ma'a Nonu running at Carter all day - who doesn't want to see that?

Without spoiling the anticipation, it's probably not going to happen that often. In this Chalkboard I will explain, 1. Why the Crusaders defensive system will mitigate against those two meeting often head-to-head, and 2. How the Blues might manipulate their attack to involve Carter more on defence than the Crusaders would like.

1. There are three main types of defensive systems. There's the drift or one-out system, the man-on system and the outside-to-in, more commonly known as the umbrella system, where the outsides come up and in, getting in the peripheral vision of the inside ball distributors and discouraging them from going wide.

The Crusaders are brilliant exponents of the drift system. They will occasionally change it up to man-on, but more of than not they rely on drift.

Imagine a scrum about 15m in from the left-hand touch on, say, the 40m line. The drift defence system would see the openside flanker and halfback take care of the first receiver - usually the first-five - and everyone else drift out one. This would have Carter taking the Blues centre, Ryan Crotty the wing and so on.

In this system, the fullback shouldn't have to make a tackle unless there is a linebreak. He is cover for this and the kick through the line.

The dynamics change if the blindside wing comes into the line at first- or second-receiver. The defensive system has to quickly recognise where he is injecting himself into the backline and adjust.

It is a system that relies entirely on trusting your inside man to do his job. When the drift defence fails it is invariable because someone has panicked and come up out of the line. Carter is a smart defender, I'm not expecting this to happen with him.

In a nutshell, should the Crusaders system work properly, Carter will rarely be tackling Nonu. Unless...

2. If I was on the Blues coaching staff, I'd be looking to make as much work for Carter on defence. That might mean aligning Nonu at centre from some set-piece ball, effectively matching him up directly on Carter.

Even when they're not running Nonu at Carter, I expect they'll be asking Charlie Piutau and Pita Ahki to run hard at Carter.

If you look the Crusaders' backline, Andy Ellis, Colin Slade and Carter at 9, 10 and 12 are all excellent tacklers, but they're not aggressive defenders. Watch for the Blues to send a lot of traffic, big men at that, down those channels all night.

It should make for compelling viewing.